Luminescent perovskite nanoparticles

Abstract

To provide a perovskite type light-emitting nanoparticle with improved PLQY.SOLUTION: The present disclosure provides a perovskite type light-emitting nanoparticle, wherein, a half-value width of a peak corresponding to (110) plane in a powder X-ray diffraction pattern measured using CuKα rays is 0.53-5.5°, and it contains an organic cation as an A site cation.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to luminescent perovskite nanoparticles. [Background technology]

[0002] Perovskite-type luminescent nanoparticles have excellent optical and electronic properties and are therefore expected to be applied in many fields, including organic light-emitting diodes (LEDs), solar cells, laser light sources, micro LED displays, liquid crystal displays, and UV sensors (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-525671 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is still room for improvement in the photoluminescence quantum yield (PLQY) of luminescent perovskite nanoparticles. [Means for solving the problem]

[0005] The luminescent nanoparticles of the present invention are perovskite-type luminescent nanoparticles, which have a half-width of 0.53 to 5.5° of the peak corresponding to the (110) plane in a powder X-ray diffraction pattern measured using CuKα radiation, and contain an organic cation as an A-site cation.

[0006] The luminescent nanoparticles of the present invention may be perovskite-type luminescent nanoparticles, in which the half-width of the peak corresponding to the (100) plane in the powder X-ray diffraction pattern measured using CuKα radiation is 0.55 to 1.1°, and which contain an organic cation as the A-site cation.

[0007] The luminescent nanoparticles of the present invention are perovskite-type luminescent nanoparticles, in which the half-width of the peak corresponding to the (200) plane in the powder X-ray diffraction pattern measured using CuKα radiation is 0.55° to 1.5°, and which may contain an organic cation as the A-site cation.

[0008] In the above-mentioned luminescent nanoparticles, it is preferable that 60 mol % or more of the A-site cations are at least one selected from the group consisting of ammonium cations, guanidium cations, imidazolium cations, pyridinium cations, pyrrolidinium cations, and protonated thiourea cations. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide luminescent perovskite nanoparticles with improved PLQY. DETAILED DESCRIPTION OF THE INVENTION

[0010] The luminescent nanoparticles of this embodiment are perovskite-type luminescent nanoparticles, contain organic cations as A-site cations, and satisfy at least one of the conditions (1) to (3). (1) The half-value width of the peak corresponding to the (110) plane in the powder X-ray diffraction pattern is 0.53 to 5.5°. (2) The half-width of the peak corresponding to the (100) plane in the powder X-ray diffraction pattern is 0.55 to 1.1°. (3) The half-value width of the peak corresponding to the (200) plane in the powder X-ray diffraction pattern is 0.55 to 1.5°. The luminescent nanoparticles preferably satisfy two or more of the conditions (1) to (3), and preferably satisfy all of the conditions (1) to (3). In this specification, the half width means the full width at half maximum. In addition, the powder X-ray diffraction pattern is expressed by the diffraction angle (2θ) on the horizontal axis. In this specification, the powder X-ray diffraction pattern is measured using CuKα radiation (wavelength: approximately 0.15418 nm).

[0011] The lower limit of the half-width of the peak corresponding to the (110) plane in the powder X-ray diffraction pattern is 0.53°, preferably 0.55°, and the upper limit of the half-width of the peak corresponding to the (110) plane in the powder X-ray diffraction pattern is 5.5°, preferably 4°, more preferably 2°, even more preferably 1.5°, and particularly preferably 1.1°.

[0012] The lower limit of the half-width of the peak corresponding to the (100) plane in the powder X-ray diffraction pattern is 0.55°, preferably 0.56°, and the upper limit of the half-width of the peak corresponding to the (100) plane in the powder X-ray diffraction pattern is 1.1°, preferably 1.0°, more preferably 0.9°, even more preferably 0.8°, and particularly preferably 0.75°.

[0013] The lower limit of the half-width of the peak corresponding to the (200) plane in the powder X-ray diffraction pattern is 0.55°, preferably 0.56°, and more preferably 0.57°, and the upper limit of the half-width of the peak corresponding to the (200) plane in the powder X-ray diffraction pattern is 1.5°, preferably 1.3°, more preferably 1.2°, even more preferably 1.0°, and particularly preferably 0.9°.

[0014] In powder X-ray diffraction measurements, corrections such as background correction, smoothing, and kα2 removal may be performed on the acquired data.

[0015] The luminescent nanoparticles of this embodiment are perovskite-type luminescent nanoparticles, i.e., compounds represented by the general formula ABX3. Here, A is a chemical species occupying the A site (i.e., A-site cation), B is a chemical species occupying the B site (i.e., B-site cation), and X is a chemical species occupying the X site. Note that although the terms A-site cation and B-site cation have formal charges of +1 and +2, respectively, they merely refer to the chemical species at the A and B sites, and the actual compounds may not necessarily have the same charges as the formal charges.

[0016] The A-site cation is at least one of an organic cation and an inorganic cation. The inorganic cation includes an alkali metal ion. The alkali metal ion is Cs + , Rb + , K. + , Na + , and Li + Examples include:

[0017] Examples of organic cations at the A site include nitrogen-containing organic cations, such as at least one cation selected from the group consisting of ammonium cations, amidinium cations, guanidium cations, imidazolium cations, pyridinium cations, pyrrolidinium cations, and protonated thiourea cations. More specifically, examples include cations represented by the following formulas (A-1) to (A-7), namely, primary to quaternary ammonium cations (A-1) (excluding those represented by (A-2)), pyrrolidinium cations (A-2), amidinium cations (A-3), guanidinium cations (A-4), imidazolium cations (A-5), pyridinium cations (A-6), and protonated thiourea cations (A-7).

[0018] [ka]

[0019] In formula (A-1), R each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a phenyl group, a benzyl group, a phenethyl group, a halogen atom, or a pseudohalogen, or two R together form an alkylene group having 2 to 6 carbon atoms. When R is an alkyl group, examples of R include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, and a tert-butyl group. When two Rs combine to form an alkylene group having 2 to 6 carbon atoms, examples of the alkylene group include an ethylene group, an n-propylene group, and a 2,2-dimethylpropylene group. Examples of the cation represented by formula (A-1) include benzylammonium cation, iso-butylammonium cation, n-butylammonium cation, t-butylammonium cation, diethylammonium cation, dimethylammonium cation, ethylammonium cation, methylammonium cation (MA), phenethylammonium cation, isopropylammonium cation, and n-propylammonium cation, with the methylammonium cation being preferred.

[0020] In formulas (A-2) to (A-7), R 2 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. A methyl group or an ethyl group is preferred, and a methyl group is more preferred. 2 If there are multiple R 2 may be different from each other or may be the same. In formula (A-3), R 1 represents a methyl group, a hydrogen atom, a halogen atom, or a pseudohalogen. Examples of the cation of formula (A-3) include an acetamidinium cation and a formamidinium cation (FA), with the formamidinium cation being preferred. Examples of the cations of formula (A-2) and formulas (A-4) to (A-7) include pyridinium cation, guanidinium cation, imidazolium cation, 1-methylimidazolium cation, pyridinium cation, 1-methylpyridinium cation, and protonated thiourea cation.

[0021] At least 60 mol % of the A-site cations may be at least one selected from the group consisting of ammonium cations, guanidium cations, imidazolium cations, pyridinium cations, pyrrolidinium cations, and protonated thiourea cations. At most 40 mol % of the A-site cations may be amidinium cations, preferably at most 30 mol %, and more preferably at most 20 mol %. The A-site cations may not necessarily be amidinium cations.

[0022] In particular, the A-site cation is preferably an ammonium cation, more preferably a primary ammonium cation having an alkyl group having 1 to 4 carbon atoms, and even more preferably a methylammonium cation. Ammonium cations preferably account for 60 mol % or more, preferably 70 mol % or more, and more preferably 80 mol % or more of the A-site cations.

[0023] Examples of B-site cations include cations of metal elements selected from Ge, Sn, Pb, Sb, Bi, Cu, Ni, Co, Fe, Mn, Cr, Pd, Cd, Eu, Yb, Ag, etc., and the cation of Pb or Sn is preferred. There may be only one type of B-site cation, or two or more types.

[0024] X is a chemical species occupying the X site. The X site is a site located at the vertex of an octahedral structure centered on the element located at the B site, and corresponds to the site where oxygen exists in a perovskite oxide. Examples of X include Cl, Br, I, -CN (cyanide), -SCN (thiocyanate), -NSC (isothiocyanate), and -S (sulfide), which may exist as anions or may be coordinately bonded to the element occupying the B site. X is preferably Cl, Br, or I. The luminescent nanoparticles may contain one or more chemical species as X.

[0025] A, B, and X can be appropriately selected in consideration of the potential within the luminescent nanoparticle, the size of the atoms contained in A, B, and X, and the like.

[0026] The luminescent nanoparticles may be surface-treated with a surfactant. The surfactant is not particularly limited and may be any of a nonionic surfactant, a cationic surfactant, a zwitterionic surfactant, and an anionic surfactant.

[0027] The surfactant is preferably an amine compound, a quaternary ammonium salt, or a carboxylic acid having 8 to 30 carbon atoms.

[0028] The carbon number of the carboxylic acid as a surfactant is preferably 10 to 25, and more preferably 12 to 20. The carboxylic acid may be a monocarboxylic acid or a polycarboxylic acid. The carboxyl groups of the carboxylic acid may be partially or completely neutralized (that is, partially or completely may be in the form of a salt). The salt of the carboxylic acid is not particularly limited, but examples thereof include alkali metal salts. The carboxylic acid as a surfactant may be either an aromatic carboxylic acid or an aliphatic carboxylic acid, but is preferably an aliphatic carboxylic acid. The aliphatic carboxylic acid is preferably a fatty acid. The fatty acid preferably has 8 to 30 carbon atoms, more preferably 12 to 20 carbon atoms. Specific examples of the fatty acid include oleic acid, stearic acid, palmitic acid, etc., with oleic acid being preferred. Examples of the salt of the fatty acid include alkali metal salts. Examples of aromatic carboxylic acids include 3-phenylpropionic acid, 4-phenyl-3-butenoic acid, phenylacetic acid, and benzoic acid.

[0029] The amine compound as a surfactant may be any of a primary amine compound, a secondary amine compound, and a tertiary amine compound, and may be either an aromatic amine or an aliphatic amine. Examples of the hydrocarbon group contained in the amine compound as a surfactant include an alkyl group, an alkenyl group, an aryl group, and a cycloalkyl group, and the alkyl group is preferred. The alkyl group may be a linear or branched alkyl group. The aliphatic amine compound is preferably a primary aliphatic monoamine compound. Examples of the primary aliphatic amine compound include primary aliphatic amine compounds having an aliphatic hydrocarbon group having 2 to 20 carbon atoms, more specifically, propylamine, butylamine, pentylamine, octylamine, hexadecylamine, octadecylamine, etc., with octylamine being preferred. Examples of the aliphatic amine compound also include aliphatic diamines such as 1,8-octyldiamine. Examples of aromatic amines include benzylamine, phenethylamine, 3-phenyl-2-propen-1-amine, phenylmethylamine, 2,2'-iminodibenzoic acid, aniline, 3-phenylpropylamine, and 4-phenylbutylamine. Examples of quaternary ammonium salts as surfactants include aliphatic quaternary ammonium salts, such as didodecyldimethylammonium and 3-(N,N-dimethyloctadecylammonio)propanesulfonate.

[0030] The surfactant may contain a phosphorus-containing compound such as phosphonic acid or phospholipid. Examples of phosphonic acid include octylphosphonic acid and tetradecylphosphonic acid. Examples of phospholipid include trioctylphosphine oxide. The surfactant may also contain alkylthiol. The alkylthiol may be an alkylthiol having 6 to 20 carbon atoms, and specific examples include 1-octanethiol.

[0031] The luminescent nanoparticles may be surface-treated with a metal halide compound. Examples of the metal halide compound include metals other than the B-site metals, more specifically, Zn, Mn, Ga, In, etc. Examples of the metal halide compound include ZnBr2, MnBr2, GaBr2, InBr2, etc. When modified with a metal halide compound, the luminescent nanoparticles are preferably those in which the chemical species occupying the A-site is a metal element.

[0032] The luminescent nanoparticles of this embodiment have an excellent PLQY. As shown in Patent Document 1 and the like, conventional perovskite-type luminescent nanoparticles have a very small half-width of the peak corresponding to the (110), (100), or (200) plane in the powder X-ray diffraction pattern, e.g., about 0.1°. However, after extensive research, the present inventors have found that the PLQY is actually improved when the half-width of the peak corresponding to the (110), (100), or (200) plane in the powder X-ray diffraction pattern is in a range larger than conventional values ​​(i.e., within the range of conditions (1) to (3)). The reason for this is not entirely clear, but it is believed that the widening of the half-width indicates the formation of an amorphous structure, and that the amorphous state of the nanocrystal surface acts as a passivation layer, thereby improving the PLQY.

[0033] The method for producing the perovskite-type luminescent nanoparticles of this embodiment is not particularly limited, but they can be produced, for example, by the LARP method (Ligand Assisted Reprecipitation).

[0034] In the LARP method, a precursor solution is first prepared by dissolving raw materials and ligands in a good solvent. Next, a poor solvent is added to the precursor solution to precipitate luminescent nanoparticles. Adding the poor solvent to the precursor solution in a batchwise manner in a single reaction vessel makes it easier to obtain luminescent nanoparticles that satisfy at least one of the above conditions (1) to (3).

[0035] Examples of raw materials for luminescent nanoparticles include raw materials containing A-site chemical species, raw materials containing B-site chemical species, and compounds containing X-site chemical species. The raw materials for luminescent nanoparticles may be any material that can provide any of A, B, and X in the general formula ABX3, and may contain multiple A, B, and X chemical species.

[0036] Examples of raw materials containing A-site chemical species include compounds containing A-site chemical species and X. For example, when the A-site cation contains an alkali metal ion, the raw material containing the A-site cation is preferably a salt of an alkali metal and X, and is preferably an alkali metal halide, but may also be a compound that does not contain X, such as an alkali metal carbonate or alkali metal acetate.

[0037] When the chemical species at the A site is an organic cation, examples of the raw material containing the chemical species at the A site include salts of the organic cation and X. More specifically, examples of the raw material containing the chemical species at the A site include at least one compound selected from the group consisting of ammonium salts, amidinium salts, guanidinium salts, imidazolium salts, pyridinium salts, pyrrolidinium salts, and salts of protonated thiourea. These salts are preferably halide salts, and more preferably bromide salts, iodide salts, or chloride salts. Examples of the raw material containing the chemical species at the A site include ammonium halide salts such as methylammonium bromide, and formamidinium halide salts such as formamidinium bromide.

[0038] Examples of raw materials containing B-site cations include B-site metal-containing compounds, such as salts of B-site cations and X. The B-site metal-containing compound is preferably a compound containing at least one metal element selected from the group consisting of Ge, Sn, Pb, Sb, Bi, Cu, Ni, Co, Fe, Mn, Cr, Pd, Cd, Eu, Yb, and Ag. More specifically, examples of B-site metal-containing compounds include halides (fluorides, chlorides, bromides, or iodides) of Ge, Sn, Pb, Sb, or Bi, with bromides, iodides, or chlorides of Ge, Sn, Pb, Sb, or Bi being preferred.

[0039] Compounds containing X-site species include compounds containing the above-mentioned A-site or B-site species and X-site species, as well as compounds that do not contain either A-site or B-site species, such as HCl and HI.

[0040] Examples of the ligand include those exemplified as surfactants above. However, when an aliphatic monoamine (preferably having an alkyl group with 3 to 16 carbon atoms) or an aromatic amine is used in combination with a carboxylic acid with 8 to 30 carbon atoms, luminescent nanoparticles that satisfy at least one of the above conditions (1) to (3) are easily obtained. The alkyl group carried by the aliphatic monoamine as a ligand may be either a branched or linear alkyl group, but a linear alkyl group is preferred. The number of carbon atoms carried by the alkyl group carried by the aliphatic monoamine is preferably 3 to 16, more preferably 4 to 12, and even more preferably 4 to 8. Specific examples of the alkyl group carried by the aliphatic monoamine include an n-propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group.

[0041] Examples of aromatic amines used as ligands include amines having an aryl group, and particularly preferred are amines having a phenyl group or a substituted phenyl group. Among these, compounds having a structure in which a phenyl group or a substituted phenyl group is linked to a nitrogen atom via an alkylene group having 2 to 6 carbon atoms are preferred, and specifically, 2-phenylethylamine, 3-phenylpropylamine, and 4-phenylbutylamine are preferred, with 2-phenylethylamine being particularly preferred. Substituents possessed by the substituted phenyl group include halogen atoms and the like. The substituted phenyl group preferably has one or two substituents per phenyl group. Examples of aromatic amines having a substituted phenyl group include those in which the hydrogen atom of the phenyl group is substituted with a substituent (e.g., a halogen atom), such as 2-phenylethylamine, 3-phenylpropylamine, and 4-phenylbutylamine.

[0042] The carboxylic acid as a ligand is preferably a carboxylic acid having 8 to 30 carbon atoms, more preferably a carboxylic acid having 10 to 20 carbon atoms, and even more preferably a carboxylic acid having 12 to 20 carbon atoms. Specific examples of the carboxylic acid as a ligand include oleic acid, stearic acid, palmitic acid, etc.

[0043] Good solvents include those in which the solubility (25° C.) of the raw material is 1 g / L or more, and specific examples thereof include N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF).

[0044] Examples of poor solvents include those having a solubility (25°C) of less than 1 g / L for the raw materials, and specific examples include hydrocarbon solvents such as toluene, hexane, and octadecene, and halogenated hydrocarbon solvents such as chlorobenzene and chloroform. The solubility of the poor solvent for the raw materials is preferably 10 mg / L or less, and more preferably 1 mg / L or less.

[0045] The amount of poor solvent used is preferably 10 times or more, more preferably 15 times or more, in terms of volume ratio to the precursor solution, from the viewpoint of being able to prevent re-dissolution of the luminescent nanoparticles after they have been precipitated.

[0046] The amount of ligand used (added amount) is not limited as long as it is equal to or less than the saturation solubility (the maximum amount of surfactant that can dissolve in the dispersion medium at the reaction temperature), and is preferably 1% by mass or less relative to the total amount of raw materials for the luminescent nanoparticles. The ligands used during production may be removed from the luminescent nanoparticles by washing after production, or the ligands may be almost completely removed. Furthermore, from the viewpoint of suppressing aggregation of the luminescent nanoparticles, the luminescent nanoparticles may be surface-treated with another surfactant after ligand removal. Furthermore, a surfactant may be added to the obtained luminescent nanoparticles for further surface treatment without removing the ligands.

[0047] The molar ratio of the raw material containing the A-site chemical species to the raw material containing the B-site chemical species in the mixture is not particularly limited, but the raw material containing the B-site chemical species can be used in excess of the raw material containing the A-site chemical species. For example, the molar ratio of the A-site chemical species to the B-site chemical species is preferably 1.0:1.0 to 1.0:35, and more preferably 1.0:1.0 to 1.0:7. The raw material containing the A-site chemical species can also be used in excess of the raw material containing the B-site chemical species. In this case, the molar ratio of the A-site chemical species to the B-site chemical species is preferably 1.0:1.0 to 70:1.0, and more preferably 1.0:1.0 to 14:1.0.

[0048] The resulting luminescent nanoparticles can be collected by a separation method such as decantation, filtration, or centrifugation.

[0049] The luminescent nanoparticles of this embodiment can be used in organic LEDs, solar cells, laser light sources, micro LED displays, liquid crystal displays, UV sensors, and the like. The luminescent nanoparticles of this embodiment can be used as a composition containing the luminescent nanoparticles and a binder. Examples of the binder include resins, which may be either thermoplastic resins or thermosetting resins. To improve dispersibility in the binder, the surfaces of the luminescent nanoparticles of this embodiment may be surface-modified with a dispersant such as a silane coupling agent. [Example]

[0050] (Manufacturing Examples 1 to 7) As raw materials, 3.6 mg of methylammonium bromide and 14.7 mg of lead(II) bromide were dissolved in 1 mL of N,N-dimethylformamide, and 4 μL of an amine compound shown in Table 1 and 5 μL of oleic acid were added as ligands to prepare a precursor solution. The obtained precursor solution was added to chloroform in a volume ratio of 25 times, to obtain a dispersion liquid in which luminescent nanoparticles were dispersed.

[0051] [Table 1]

[0052] The dispersions obtained in Production Examples 1 to 7 were centrifuged at 9000 rpm for 10 minutes. After centrifugation, the precipitate layer was collected from the dispersion, applied to a glass plate, and dried overnight to obtain a measurement sample. The powder X-ray diffraction pattern was measured using the above measurement sample. The equipment used was a "SmartLab 9kW" fully automated multipurpose X-ray diffractometer manufactured by Rigaku Corporation, and the radiation source used was CuKα radiation. The acquired powder X-ray diffraction measurement data was imported into Rigaku's integrated powder X-ray analysis software, and subjected to background correction, smoothing, and kα2 removal. The results are shown in Table 2.

[0053] The fluorescence intensity of the luminescent nanoparticles was measured using a fluorescence spectrophotometer (HORIBA, product name: FluoroMax-2) to determine the wavelength of the emission peak of the luminescent nanoparticles. PLQY was also measured using an absolute PL quantum yield analyzer (Hamamatsu Photonics, product name: C9920-01). The results are shown in Table 2.

[0054] [Table 2]

Claims

1. General formula ABX ３ Luminescent perovskite nanoparticles containing a compound represented by the formula: The half-width of the peak corresponding to the (110) plane in the powder X-ray diffraction pattern measured using CuKα radiation is 0.53 to 2°, containing a nitrogen-containing organic cation as an A-site cation; containing at least one cation of Pb and Sn as a B-site cation; Luminescent nanoparticles, wherein X comprises Cl, Br, or I.

2. General formula ABX ３ Luminescent perovskite nanoparticles containing a compound represented by the formula: the half-width of the peak corresponding to the (100) plane in the powder X-ray diffraction pattern measured using CuKα radiation is 0.55 to 0.9°; containing a nitrogen-containing organic cation as an A-site cation; containing at least one cation of Pb and Sn as a B-site cation; Luminescent nanoparticles, wherein X comprises Cl, Br, or I.

3. General formula ABX ３ Luminescent perovskite nanoparticles containing a compound represented by the formula: the half-width of the peak corresponding to the (200) plane in the powder X-ray diffraction pattern measured using CuKα radiation is 0.55 to 1.2°; containing a nitrogen-containing organic cation as an A-site cation; containing at least one cation of Pb and Sn as a B-site cation; Luminescent nanoparticles, wherein X comprises Cl, Br, or I.

4. The luminescent nanoparticle according to any one of claims 1 to 3, wherein 60 mol% or more of the A-site cations are at least one selected from the group consisting of ammonium cations, guanidium cations, imidazolium cations, pyridinium cations, pyrrolidinium cations, and protonated thiourea cations.

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